Disable size_t truncation warning (C4267) on BoringSSL Win64.

third_party/boringssl/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # Config for us and everybody else depending on BoringSSL.
 config("openssl_config") {
   include_dirs = []
   include_dirs += [ "src/include" ]
   if (is_component_build) {
     defines = [
@@ skipping 43 matching lines @@
 
   # Also gets the include dirs from :openssl_config
   include_dirs = [
     "src/include",
     # This is for arm_arch.h, which is needed by some asm files. Since the
     # asm files are generated and kept in a different directory, they
     # cannot use relative paths to find this file.
     "src/crypto",
   ]
 
+  if (is_win) {
+    # TODO(davidben): Fix size_t truncations in BoringSSL.
+    # https://crbug.com/429039
+    cflags += [ "/wd4267"]
+  }
+
   if (cpu_arch == "x64") {
     if (is_mac) {
       sources += gypi_values.boringssl_mac_x86_64_sources
     } else if (is_linux || is_android) {
       sources += gypi_values.boringssl_linux_x86_64_sources
     } else if (is_win) {
       sources += gypi_values.boringssl_win_x86_64_sources
     } else {
       defines += [ "OPENSSL_NO_ASM" ]
     }
   } else if (cpu_arch == "x86") {
     if (is_mac) {
       sources += gypi_values.boringssl_mac_x86_sources
     } else if (is_linux || is_android) {
       sources += gypi_values.boringssl_linux_x86_sources
     } else if (is_win) {
       deps += [ ":boringssl_asm" ]
     } else {
       defines += [ "OPENSSL_NO_ASM" ]
     }
   } else if (cpu_arch == "arm") {
     sources += gypi_values.boringssl_linux_arm_sources
   } else {
     defines += [ "OPENSSL_NO_ASM" ]
   }
 }